Preventive capacity of allergen immunotherapy on the natural history of allergy

Allergen immunotherapy (AIT) is the practice of administering gradually increasing doses of the specific causative allergen to reduce the clinical reactivity of allergic subjects. A bulk of literature demonstrates that AIT is an effective and safe treatment to reduce allergic symptoms and the use of drugs. The preventive capacity of AIT is less investigated. The studies thus far available showed that this treatment, in both forms of subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) is able to prevent the development of asthma in patients with allergic rhinitis and the occurrence of new sensitizations in patients monosensitized. Such outcomes demonstrate the ability of AIT to change the natural history of respiratory allergy. Of particular importance, SCIT with Hymenoptera venom has an invaluable role in preventing potentially fatal anaphylactic reactions to the culprit sting in venom-allergic patients. Ongoing studies are aimed at evaluating the possible capacity of AIT in primary prevention of allergy. All these capabilities are related to the mechanisms of action of AIT. In fact, both SCIT and SLIT are able to modify the allergen presentation by dendritic cells that in turn modify the phenotype of allergen-specific T cells, switching from the Th2-type response, typical of allergic inflammation, to a Th1-type response. An important role is played by allergen-specific T regulatory (Treg) cells, which produce suppressive cytokines such as IL-10 and TGF-beta.